In an electrophotographic image forming apparatus such as a laser printer, an electrostatic copying machine, a plain paper facsimile machine or a printer-copier-facsimile multifunction machine, a charging roller is used for uniformly electrically charging a surface of a photoreceptor body.
The charging roller typically includes a roller body having a single layer structure or a multilayer structure including a layer produced, for example, by preparing a semiconductive rubber composition containing an ion conductive rubber (e.g., epichlorohydrin rubber) as a rubber component, forming the semiconductive rubber composition into a tubular body and then crosslinking the rubber component of the tubular body.
Incidentally, fine particles such as external additive particles externally added to toner or finely broken toner particles occurring when image formation is repeatedly performed are liable to adhere to an outer peripheral surface of the roller body to be transferred from the outer peripheral surface to a formed image, resulting in defective image formation. For suppression of the adhesion of the fine particles, it is a general practice to condition the outer peripheral surface, for example, by wet-polishing the outer peripheral surface and/or coating the outer peripheral surface with a coating film.
However, the coating film is formed by applying a liquid coating agent onto the outer peripheral surface of the roller body by a spraying method, a dipping method or other coating method, and then drying the applied liquid coating agent. Therefore, the coating film is liable to suffer from contamination with foreign matter such as dust, uneven thickness and other defects during the forming process.
For preparation of the coating agent, an organic solvent is required. The use of the organic solvent may exert a great load on the environment, and go against a recent trend toward reduction of VOC (volatile organic compounds).
It is also contemplated to form an oxide film instead of the coating film by finishing the outer peripheral surface of the roller body formed from the rubber composition by a wet polishing method or the like, and oxidizing the rubber composition present in the outer peripheral surface (finish-polished surface) by irradiating the outer peripheral surface with ultraviolet radiation in an oxidizing atmosphere, and to prepare a rubber composition suitable for the formation of the oxide film (see Patent Documents 1 and 2).
A known example of the rubber composition suitable for the formation of the oxide film is a rubber composition containing the aforementioned ion conductive rubber as well as diene rubber which is oxidizable to form the oxide film by the irradiation with the ultraviolet radiation.